It is widely known that sodium styrene sulfonate can be synthesized by reacting an aqueous β-haloethylbenzene sulfonic acid solution with an aqueous sodium hydroxide solution.
For example, Patent Document 1 discloses a method of reacting an aqueous sodium hydroxide solution and an aqueous β-bromoethylbenzene sulfonic acid solution at 60° C. or higher, followed by cooling to precipitate sodium styrene sulfonate.
Further, by using an aqueous lithium hydroxide solution instead of the aqueous sodium hydroxide solution, and reacting it with an aqueous β-bromoethylbenzene sulfonic acid solution, followed by cooling, it is possible to obtain lithium styrene sulfonate.
However, lithium styrene sulfonate by this method has a strong affinity for water, and therefore, in order to increase the purity, it is necessary, after solid-liquid separation, to conduct drying under atmospheric pressure or reduced pressure at a temperature of at least 40° C., whereby there has been a problem that the load for drying is substantial and the production cost is high. Further, drying by heating tends to promote polymerization of lithium styrene sulfonate, thus leading to a problem such that the lithium styrene sulfonate is likely to be polymerized.